Black and Gold Aposematic Ants
In 1927, entomologist Alexander Nicholson first proposed that widespread mimicry across species, known as ‘mimetic complexes’, existed in Australian invertebrates. Such complexes have been widely recorded in wasps and in some butterfly species, but have previously not been studied in ants. Pekár et al. studied Australian ants and the insects that mimic them, finding that more than 140 arthropod species, including 126 ant species, 7 spider species, 3 true bug species, one wasp, and one treehopper, use varying gold and black dorsal colouration to warn off predators. Some of these ant-like mimics also employed other defences, such as unpalatable chemicals or spines. Using colouration to deter would-be predators, known as ‘aposematism’, is a well-known defence strategy that either warns of actual toxicity or mimics the ‘advertising’ of unpalatable or toxic species. Warning signals and mimicry are likely to have evolved alongside toxicity or lack of palatability. Consequently, the more apparent the warning or the better the mimicry, the more distasteful the species should be to predators. Predators of the look-alike species were found to avoid preying on the black and gold ants or mimics if given a choice. The study used next-generation sequencing to examine the faeces or stomach contents of natural predators of the ants or ant-mimics in the wild to determine whether they consumed the black and gold species. Predators studied included 553 spiders, 50 skinks, and 48 birds. Black and gold ‘mimicking’ insects were also offered as prey to a lizard and two spider species (one ant-specialist and one ant-averse); all but one – the ant-specialist predator – preferred to eat the offering that was not black and gold. The finding adds to the small number of sizable cross-order complexes on record. Furthermore, this cross-order mimicry complex contains more species than those known among Australian fish or millipedes, although still fewer than the complex recognised in mutillid wasps.
Recent Fire Suits Breeding Gouldian Finches
Changing fire regimes since European settlement have been implicated in the decline of endangered Gouldian finches (Erythrura gouldiae), which are endemic to the fire-prone savannas of northern Australia and are dependent on the seeds of annual speargrasses (Sorghum spp.) during the breeding season. A seven-year study that monitored breeding site preference has found that these small granivorous finches favour recently burnt sites – either burnt the dry season before or every 2–3 years – revealing a preference for a fine-grain patch-mosaic fire regime. The WA study used remote sensing of fire scars to track fire regime, and data from breeding boxes to determine site preference. Researchers found that finches favoured nest boxes in places that had experienced many small fires rather than infrequent large fires. It may be that fire both increases the nutritional value of the soil and removes older sorghum grass stalks, making old seeds that fall to the ground more accessible and new seeds more nutritious, as well as staggering the production and diversity of seed-bearing grasses. Unfortunately for the 2500 Gouldian finches left in the wild, frequent low-intensity fires have become the exception. During the study period, the mean fire tract increased from 56 ha in 2007 to 670 ha in 2015. Larger, hotter fires later in the dry season have likely resulted in decreased breeding site fidelity for Gouldian finches and have altered the composition of native grass species, thus reducing finch numbers. ‘Patch’ burns early in the dry season may help maintain this species and preserve biodiversity in Australia’s tropical savanna habitats.
Pig-Nosed Turtles 'Talk' Underwater
The pig-nosed turtle (Carettochelys insculpta) is the only member of the Carettochelyidae family and has a limited distribution in northern Australia and southern New Guinea. Until 2005, freshwater turtles were believed to be largely deaf, mute and lacking in complex social interactions. However, 47 turtle species have now been found to emit sounds that constitute audio communication, both on land and underwater and across many life stages from hatchlings to adults. Most descriptions of these vocalisations have not been published and were recorded while the reptiles were courting, nesting or hatching. Pig-nosed turtles display some social behaviour when nesting, eating and during thermoregulation, so Ferrara et al. hypothesised that pig-nosed turtles might also vocalise. They used underwater recording devices (hydrophones) to monitor seven pig-nosed turtles in the Northern Territory in 2014. Two (a male and a female) were monitored in the field and five more (three females and two males) were recorded in a Darwin breeding facility. They captured 182 sounds across three sound categories, similar to those made by other turtle species and characteristic of contact calls. Analysis has revealed that the sounds included harmonic and non-harmonic calls as well as pulses that varied from 0.02 seconds to 0.4 seconds duration. Records of turtles’ vocal repertoires may help in comparative studies between species, but they might also one day allow for aquatic sampling. Long-term underwater recording may enable researchers to use voice recognition software to non-invasively assess the distribution and abundance of aquatic turtle species based on their vocal repertoires.
Iron and Acid Link to Whale Strandings
Tasmania has an unfortunate history of toothed whale strandings, with some 680 mass stranding events over 200 years. But why? Environmental factors from oceanography to winds, to seismic activity and sonar disruption have been implicated. Now, Nash et al. believe that iron-rich dust blowing into southern waters and increasing algal blooms could cause acid poisoning that alters whales’ navigational ability. Pseudo-nitzschia is a planktonic organism known to respond to increased marine nutrient concentrations with a resultant algal bloom. Recent studies conducted on iron fertilisation in the Southern Ocean revealed that increased iron stimulated Pseudo-nitzschia growth. Although once thought to be non-toxic, it is now recognised that algal blooms of this diatomic organism create domoic acid (DA). DA is a neurotoxin that can cause amnesic shellfish poisoning in humans and neurological dysfunction in sea lions and fur seals, specifically hippocampic lesions that potentially disrupt spatial orientation. Furthermore, DA is known to transfer through marine food webs to cetaceans, having been found in the faeces of humpback whales and blue whales. The team analysed the frequency of whale strandings in Tasmania from 1965, cross correlating strandings with dust activity using Dust Storm Index records from the Australian Bureau of Meteorology and with ocean chlorophyll levels as proxy for phytoplanktonic growth. They found that most strandings occurred during summer, when chlorophyll concentrations were also at their highest (from November to February). Dust activity was also increased at that time. The strong correlations support the hypothesis of a causative link between increased DA from iron-rich dust events and mass whale strandings, although more robust multidisciplinary research is required, including post mortem testing of stranded cetaceans for the presence of DA and bio-monitoring to confirm algal blooms of Pseudo-nitzschia whenever mass stranding events occur.
Woylie Scats and Parasitic Stressors
Woylies (brush-tailed bettongs, Bettongia penicillata) were once widespread across much of Australia but are now critically endangered and exist in remnant populations in WA. It has been suggested that the effects of parasitic infections could be exacerbated by stress and may be an important contributing factor to this decline. Stephanie Hing and colleagues studied a captive population of adult woylies (nine females and six males) at Native Animal Rescue, Malaga, WA, where the animals had access to underground fungi, native forage, insects and year-round supplementary feeding of fruit and vegetables. They measured the concentration of faecal cortisol metabolites (FCM) as a non-invasive method of examining the relationship between stress physiology and season, sex, reproductive status and the presence of parasites. Stress levels were highest in autumn and winter, even though the woylies were supplementary fed; this may be associated with circadian rhythms, shortened day length, or increased metabolic demands. Female woylies had higher mean levels of FCM than males, regardless of their reproductive status, a pattern that has also been found in the bilby, koala and southern brown bandicoot, indicating that stress-induced inhibition of reproduction is at least not a major concern in woylies. A weak but significant relationship was found between high FCM and poor body condition when parasites were present. When animals were shedding oxyurid pinworm eggs, they also had higher mean FCM levels, possibly indicating increased stress from parasite infestation, although the relationship between stress physiology and multiple parasite infections was found to be complex, warranting further study.
Sex and Age Determine Transport Costs of Seals
Pinnipeds such as seals and sea lions often travel large distances, swimming submerged, to feed. How deep seals and sea lions can dive, and for how long, depends on the metabolic cost of the activity and on how much oxygen is available to them, which should increase as these marine mammals grow. Younger otariid seals have lower oxygen stores because of their size and reduced iron intake. Australia’s three native pinniped species – the Australian fur seal, New Zealand fur seal, and Australian sea lion – often share habitat, but each species prefers different prey and exhibits different foraging strategies. Australian sea lions and Australian fur seals are benthic feeders with slight variation in diet, whereas New Zealand fur seals (pictured along with Australian fur seals, above) prefer to pick off prey in the pelagic zone; thus the Australian species dive deeper and stay submerged for longer. It was thought those differences might relate to changes in metabolism and energetic needs; however, a recent cross-species study by Ladds et al. found no significant variation in metabolic costs or cost of transport among different species of otariid seals. The metabolic rates of seals and sea lions were measured at various sizes, sexes, and stages of development while the individuals engaged in several foraging strategies. The costs of transport were then calculated, defined as the energy cost of moving one unit of body mass over one unit of distance. The researchers found that the mass-specific metabolic rate of female Australian fur seals and female Australian sea lions was higher than their male counterparts, and that mass-specific metabolic rate was higher for sub-adult individuals, regardless of species. Mass- specific metabolic rate declined the longer marine mammals were submerged and costs of transport were reduced with speed – revealing that seals are physiologically at their best when swimming submerged. The findings suggest that rapid environmental change that requires further travel for foraging might most affect those individuals which are most crucial to the species’ ongoing reproductive success: young females.